Bioavailability and biogeochemical cycling of iron in glacially-influenced fjord systems of the high Arctic, Spitsbergen (Svalbard)

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Glacially derived iron is an important, yet largely unconstrained source of potentially bioavailable iron to continental shelf waters. This micronutrient may play an important role in the fertilization of primary productivity in coastal upwelling areas particularly on the large Arctic shelf. More generally, glacially derived iron may be a vital and dynamic player in the global iron cycle over glacial-interglacial timescales and in the face of climate change. This project targets the biogeochemical cycling of iron in three Arctic fjords (Spitsbergen, Svalbard) with a focus on the sources and transfer of bioavailable iron across fjord systems and its diagenetic redox cycling in fjord sediments. Specifically, we plan to test the hypothesis that (1) glacial flour from glacial meltwater discharge and proglacial runoff zones contains a large bioavailable iron component deriving from subglacial biogeochemical weathering of glacial debris; (2) the input of these iron phases to the fjords fertilizes primary productivity in the water column and supports high rates of dissimilatory iron reduction in adjacent fjord sediments; and (3) the benthic cycling of iron, encompassing multiple dissolution and re-oxidation steps, facilitates the transport of reactive iron phases across the fjords to their mouths and ultimately to the shelf. To fulfill our objectives we will combine classical (bio)geochemical analyses, particularly pore-water trace metal measurements and sequential iron extraction schemes, with a newly developed ascorbic acid extraction method which specifically targets ferrihydrite and thus allows for the determination of the bioavailable iron content, and the analysis of iron isotope signatures.